The present invention relates to a method and apparatus for attaching metal members for assembling automotive vehicle structures.
It is known that the manufacture of automotive vehicles often requires that metal members be attached to each other for forming automotive vehicle structures. Friction stir welding is one potential method of attaching metal members. Conventional friction stir welding typically requires a rotating tool to be translated along an interface between surfaces of metal members for softening or melting portions of the members at the interface. In turn, the softened or melted portions intermix and harden to form metallurgical bonds between the members. During a conventional friction stir welding process, however, substantial amounts of liquidized material may be lost or unused forming weaker bonds. Moreover, a conventional stir welding process may require relatively large amounts of time for forming metallurgical bonds. Thus, there is a need for improved techniques, fasteners or both, alternative to conventional friction stir welding for achieving high integrity attachment of a metal members.
The present invention meets these needs by providing an improved method for attaching metal members, with particular utility in the formation of components for an automotive vehicle. The method includes the steps of:
(a) providing a first metal member;
(b) contacting the first metal member with a second metal member;
(c) providing a metal fastener that is substantially symmetrical about a central axis, the metal fastener including a top radially enlarged portion, a bottom radially enlarged portion and a shank portion intermediate the thicker portions for forming a circumferential groove about the axis and fastener;
(d) rotating the metal fastener about the axis using a rotary driving apparatus;
(e) driving the metal fastener through the first member and into the second member during rotation of the fastener thereby inducing friction between the fastener, the first member and the second member for at least locally melting portions of the first member and the second member to form a flowable material that flows into the circumferential groove of the fastener and wherein the fastener is driven only partially into the second member; and
(f) solidifying the flowable material within the circumferential groove for integrally attaching the flowable material, the fastener, the first member and the second member together wherein the flowable material metallurgically bonds with at least the first member and the second member.